advanced - maureen Flashcards
forward masking subtraction method
this method takes advantage of the refractory properties of the AN to separate the neural response to the probe from the probe artifact.
a lot of artifact because its an early latency potential, measured via intracochlear electrodes
forward masking 4 parts
A. probe = response + artifact
B. Probe preceded by masker = response to masker + masker artifact + negligible probe response +probe artifact
C. Masker = Response to masker and masker artifact
D. No stim = pre amplifer
A - (b -c) - D
current level (probe)
increasing past ECAP threshold you get an amplitude growth function
extrapoliated T-NRT- predicts ecap with an amplitude of 0
how does the response grow as level increase
current level (masker)
typically makser +10 CU to elicit response and refractory perdio but you can set to +5 cu for tolerance issues
stim rate
auto 80 pps
current level stays same but not perceived as loud
get more points along the curve! q
increase stim rate you can get faster and get louder in intraoperative
decrease to get louder with tolerance or compliance issues
recording active electrode
default +2 away (apical)
can change direction and electrode offset (2 or 3)
you would move further away if you were getting a lof of artifact
amplifier gain
increasing gain can give clearer signals but increases chance of saturation and noisy responses
if its high like 60 you are more susceptible to noise. 40 is default
high enough to get response without getting noise
stimulus length
2 pw + interphase gap = stimulus
recording delay
short - you get more reponse sooner and usally better picure of the N1 slope
if you want longer you risk missing the inital deploarizign of the nerve
amplitude growth function
input output function of peak to peak amplitude as a funtion of current level
steepness if used to infer the size of suriving spiral ganglion population
100 go to 250 step size 5 until they tell you too loud
current spread - biological
more neurons the bigger response cause every one contributes its own energy
UNLESS you dont have a lot of neurons then you can increase current but still have a little response
3 age impact performance wtih CI
poor neural survival
age related auditory temporal processing
cog decline
interphase gaps
short interphase gap (7 usec) and the long interphase gap (30 usec) longer period between probe and masker phases you aer allowing more neurons that may have refractory time to recover and then fire therefore increasing n1 p1 amplitude
refractory periods get long as you age
so if there was a big difference then mauve they have the neurons but they needed longer to recover
still never grew as steep as young
